The invention relates to a display device having a plurality of pixels arranged in a matrix, and more particularly, to a display device having multiplex signal lines for transmitting a display signal to a plurality of pixels in one pixel array.
Recently, a liquid crystal display device has been used in a wide field ranging from medium-sized and large-sized displays for use in a computer, a television and the like to small-sized displays for use in a car navigation system and a cellular phone. Among the display devices, an active matrix liquid crystal display device using an active device such as a TFT (thin film transistor) or an MIM (metal insulator metal) receives attention because of its superior display characteristics. In general, the active matrix liquid crystal display device comprises a TFT array substrate having TFTs as active devices that are arranged in a matrix, an opposite substrate which is opposed to the TFT array substrate, and liquid crystal filled in-between the two substrates.
In a color liquid crystal display device, a color filter for performing color display is generally disposed on the opposite substrate. The liquid crystal display device comprises a display area composed of a plurality of pixels, each of which includes a pixel electrode and a TFT. The pixel electrode applies an electric field to liquid crystal, thereby changing light transmittance of the liquid crystal and thus displaying an image. Each of the pixels displays any one of RGB colors.
Each pixel applies an electric field to the liquid crystal in accordance with a display signal voltage inputted from a driver IC (integrated circuit). The driver IC is generally connected to the TFT through TAB (tape automated bonding), however, the driver IC may be disposed directly on a glass substrate of a TFT array. Generally, a plurality of source driver ICs for signal lines are provided on one side of the TFT array, and a plurality of gate driver ICs for gate lines for controlling gate voltages are provided on another side of the TFT array. A voltage inputted from each source driver IC is sent to each pixel electrode through source/drain electrodes of the TFT, and thus each pixel electrode applies an electric field to the liquid crystal. Changing the voltage allows a voltage being applied to the liquid crystal to change, thereby controlling the transmittance of the liquid crystal.
It is well known that the number of pixels is generally increased in order that the above-described liquid crystal display device displays a high-quality and high-definition image. It is also well known that the increase in the number of pixels causes the increase in the number of driver ICs for driving the liquid crystal display device and thus causes the increase in the cost of manufacturing the display device. Moreover, a serious problem arises that higher definition makes it more difficult to connect the driver ICs to the liquid crystal display device.
In order to facilitate terminal connection of a high-definition panel by reducing the number of signal input terminals, and also to reduce the cost of drivers, for example, an active matrix liquid crystal display using a thin film transistor (TFT), which comprises an active device serving as a switch between a signal input terminal of a TFT substrate and a signal line, is disclosed in Japanese Patent Application Laid-Open No. Hei 6 (1994)-138851.
The above-described display requires a transistor for use in a multiplex circuit, which a relatively large current can pass through. The reason is that the multiplex circuit is disposed outside a display area and one transistor is connected to each pixel array. Therefore, the display needs a transistor of a large size and thus has a problem that manufacturing yield is relatively low.
In Japanese Patent Application Laid-Open No. Hei 9 (1997)-329807, disclosed is a display device provided with a plurality of pixels arranged in a matrix in a display area, signal lines for selecting row positions, and pixel signal lines for providing each pixel information in a column direction, the display device selecting pixels in accordance with signals supplied by the signal lines and displaying the pixels in accordance with the pixel information provided to the selected pixels. A first device is provided for each pixel and operates in accordance with a signal from a signal line corresponding to each pixel. Block selecting means is provided for dividing pixels into blocks and selects the blocks into which the pixels are divided and collectively selecting the pixels included in the selected block. A second switching device is provided for each pixel and operating on the pixels corresponding to the block selected by the block selecting means. The second switching device acquires pixel information for each of the pixels with the first switching device and provides the acquired pixel information to display the pixels.
The above-described display device attempts to greatly reduce power consumption by eliminating the need to output a signal to each of the pixels that do not have to be rewritten, by selectively driving each pixel or each pixel block that is composed of a plurality of pixels. However, the display device cannot solve the above-mentioned problems to create a higher definition because the pixel signal line is provided for each pixel array.
A liquid crystal display device for multi-gradation at a low cost, which suppresses an increase in the number of components of a data line driver by making partially common use of the data line when performing multi-gradation display is constructed of a plurality of cells capable of controlling display pixels independently of one another, is disclosed in Japanese Patent Application Laid-Open No. Hei 5 (1993)-341734. The liquid crystal display device ensures that the increase in the number of components of the data line driver can be suppressed, however, the display device has a problem in that the number of gate lines is inevitably increased.